1. Technical Field of This Invention
The present invention relates to an offshore or marshland production system for use in the production of natural gas and hydrocarbon liquids.
2. The Prior Art
Currently, offshore and marshland production systems are comprised of numerous separate equipment components to perform specific functions. For example, indirect fired flow-line heaters are used to heat the flow-stream from a gas well to prevent freezing and formation of hydrates. Production separators separate the gas from condensate and produced water. Likewise, a coalescer is used to remove trace amounts of water from the condensate to satisfy market specifications and a water skimmer is used to polish produced water by removing trace amounts of hydrocarbon prior to disposing the water.
These separate components and the process function that each performs are typically installed on top of a structural steel deck and the separate components are interconnected with piping. To protect against upset conditions such as over-pressure or high liquid level, each component is equipped with safety devices such as high pressure shutdown sensors, pressure safety relief valves, and high/low liquid level shutdown sensors, etc.
Reference is made to U.S. Pat. No. 3,881,549, Production and Flare Caisson System. The Production and Flare Caisson System incorporates a vertical structural caisson into which a production separator is placed. The Production and Flare Caisson System is of limited benefit because only the production separator is placed in a vertical configuration, while the other process equipment is apparently mounted in a conventional manner on the structural deck. Utilizing these multiple components indicates the need for safety devices, such as high pressure shutdown switches, pressure safety relief valves, and high/low liquid level shutdown switches to be placed on each component and the need for these components to be interconnected with significant amounts of piping and instrumentation. Similarly, the Production and Flare Caisson System is limited in its ability to reduce the size of the structural deck, since components other than the production separator must be mounted on the structural deck. Further, the Production and Flare Caisson System makes no mention of additional value-added capabilities, such as dehydration of the gas, inlet heating of the flow-stream, polishing of the produced water or treatment of the liquid condensate.
Reference is now made to U.S. Pat. No. 4,848,475, Sea Bed Process Complex which describes a modularized oil well production complex for installation on the sea bed, which is intended to produce crude oil from oil wells. The Sea Bed Process Complex places each component into a separate "module" to facilitate installation and retrieval with sub-sea remote operated vehicles (ROV). Further, the Sea Bed Process Complex incorporates a two phase oil/gas separator utilizing a vertical annual separator in which an integral pump creates a centrifugal fluid movement which facilitates separation of the liquid and gas phases. Additionally, no mention is made in the patent for the Sea Bed Process Complex relating to dehydration of gas, heating of well-stream fluids, or polishing of produced water, which are fully described and provided for in my invention.
Reference is now made to U.S. Pat. No. 4,900,433, Vertical Oil Separator which describes a vertical separator for separating crude oil into liquid and gas phases. This patent discloses a separator which utilizes a casing design and vertical pump to impart a centrifugal or "swirling" action to flow-stream liquids, with the result that the liquid phase and gas phase of the flow-stream are separated. The Vertical Oil Separator does not accomplish heating of the inlet flow-stream, dehydration of the gas, condensate coalescing or water polishing. Further, the vessel of the Vertical Oil Separator is designed for installation below water at the sea bed and is not used as a structural component.
Reference is now made to U.S. Pat. No. 5,474,601, Integrated Floating Platform Vertical Annual Separator and Pumping System for Production of Hydrocarbons. This invention is an improvement on U.S. Pat. No. 4,900,433, in that the earlier patented device is modified and adapted for installation on a floating platform such as a tension leg platform. In addition, Patent No. 5,474,601 provides for a tensioned riser supported by a floating tension leg platform.
Reference is now made to U.S. Pat. No. 4,793,4180, Hydrocarbon Fluid Separation at an Offshore Site and Method. This invention discloses an apparatus and method for separating liquids from gas as received from large pipelines. Described in the text as a "slug catcher", the device eliminates intermittent slugs of liquids from the incoming flow-stream in order to facilitate downstream processing. This apparatus and method do not provide any capability to heat the incoming stream, separate produced water from natural gas liquids, dehydrate the natural gas, or further condition the natural gas liquids and produced water for sales or disposal, respectively. Neither is this device and method utilized as a structural component or combine the pressure vessel shell as a structural component; rather, it is installed into spare well conductor guides on existing platform structures.
Reference is now made to U.S. Pat. No. 4,506,735, Operating System for Increasing the Recovery of Fluids From a Deposit, Simplifying Production and Processing Installations, and Facilitating Operations with Enhanced Safety. This invention describes a sub-sea watertight hull configured to allow a production separator and other equipment components to be placed below the surface of the water in an atmospheric environment to facilitate production from very low pressure flow-streams by reducing hydrostatic pressures. This watertight hull allows many types of equipment components to be installed near the seabed without the disadvantages of hydrostatic pressure and inaccessibility of sub-sea installation. While the '735 patent mentions flow-stream heating, pumping, multiple stages of separation, large vessels for storage and secondary polishing, it clearly discloses these components as separate and distinct components.
Reference is made to U.S. Pat. No. 4,685,833, Offshore Structure for Deep-sea Production, which discloses an offshore structure consisting of a buoyant vessel containing a large separator for storing and separating produced fluids. The buoyant chamber provides protection for the separator, buoyancy support for the flow-lines and riser, as well as support for a deck. The '833 patent discloses a separator which is essentially a huge holding tank, with further processing being accomplished by conventional production equipment installed on top of a conventional deck. It is primarily designed for deep-water fields, taking advantage of the huge buoyant support to reduce or eliminate costly deep-water structures. The '833 patent does not disclose heating of the flow-stream, dehydration of gas, condensate coalescing or water polishing, nor does it describe a single vessel in which these functions are performed. Neither does this invention utilize the production process components as a structural support.
Reference is now made to WO 81/01310, Method and Column for Collection and Separation of Oil, Gas and Water From Blowing Wells at the Sea Bed, which discloses a method for collection of oil, gas and water from an offshore oil or gas well and a vertical column. This invention is designed to mitigate the effects of a catastrophic sub-sea well blowout by providing a means of controlling and collecting effluent discharged from the well. This invention does not address normal production functions such as gas dehydration, water polishing, condensate coalescing or well-stream heating, all of which are functions of my invention. While this invention does utilize the vessel as a structural component, the operating pressure is approximately the same as the hydrostatic head of water outside the column, rendering this device unusable for routine and continuous use as a production facility since all produced gas would have to be recompressed at high cost before flowing to gas pipelines.